The Role of Pod Corn in the Origin and Evolution of Maize

Abstract

The hypothesis which holds that cultivated maize has been derived from a wild form of pod corn at one time indigenous to the lowlands of South America is at once the oldest and among the youngest of the various propositions which have been developed to explain the origin of this unique New World cereal. More than a century ago the French naturalist, Saint-Hilaire (1829), described as a new variety Zea Mass var. tunicata, a peculiar type of maize sent to him from Brazil in which the grains were covered by the glumes. He concluded that this was the natural state of maize and that South America (Paraguay) was its native home. Virtually all students of maize since Saint-Hilaire have given serious attention to pod corn, have recognized its primitive characteristics, and have either accepted it as the ancestral form, or, for a variety of reasons, have dismissed it from this role. Their viewpoints and conclusions are reviewed and discussed in detail by Mangelsdorf and Reeves (1939). Here it will suffice to set forth the principal reasons given by various students who dismissed pod corn as the ancestral form of maize: (1) it does not breed true; (2) it apparently arises spontaneously in cultures of normal maize; (3) it is frequently monstrous; (4) it differs from normal maize primarily by a single gene; (5) the hypothesis that teosinte is the ancestral form of maize is a more plausible one. Of the five reasons given for rejecting the pod-corn hypothesis the last is particularly important, for, once the close relationship of maize and teosinte was widely recognized, the pod-corn hypothesis was relegated to a distinctly secondary role. Only recently has it again been brought into prominence by Mangelsdorf and Reeves (1939) who, on the basis of experimental evidence, concluded that teosinte, far from being the progenitor of maize, is instead the progeny of the hybridization of maize and Tripsacum. Having dismissed teosinte as the ancestral form of maize, they turned to the earlier pod-corn hypothesis as the only plausible alternative. The present paper is concerned not with the entire problem of the origin of maize but primarily with the pod-corn hypothesis, and particularly with a mass of new experimental evidence and new observations accumulated during the past ten years which have a bearing upon the problem of the role of pod corn in the origin and evolution of maize. Data previously published are included only to the extent that they are needed in presenting a complete picture; and the extensive literature on pod corn is reviewed only to the extent of providing an adequate background for the present discussion. For more detailed reviews of the literature on pod corn and for earlier data the reader is referred to Sturtevant (1899), Weatherwax (1935), and Mangelsdorf and Reeves (1939).